Water containing excess calcium and magnesium is termed as hard water. Water softening is a process by which hard water is converted to soft water. Most residential and industrial applications need soft water for prevention of scale formation on heat transfer surfaces, piping, etc… Softening is an ion exchange process where calcium and magnesium ions in the water are exchanged for sodium ions attached to the resin.

This method removes temporary and permanent hardness. Common salt is used to regenerate the resins periodically. If the brine solution is passed from the bottom of the resin and service flow is from the top, it is called up- flow softener and if the service and regeneration flows are from top to bottom, it is called co- flow softener.